An electronic device may be created from a workpiece that has undergone various processes. One of these processes may include introducing impurities or dopants to alter the electrical properties of the original workpiece. For example, charged ions, as impurities or dopants, may be introduced to a workpiece, such as a silicon wafer, to alter electrical properties of the workpiece. One of the processes that introduces impurities to the workpiece may be an ion implantation process.
An ion implanter is used to perform ion implantation or other modifications of a workpiece. A block diagram of a conventional ion implanter is shown in FIG. 1. Of course, many different ion implanters may be used. The conventional ion implanter may comprise an ion source 102 that may be biased by a power supply 101. The system may be controlled by controller 120. The operator communicates with the controller 120 via user interface system 122. The ion source 102 is typically contained in a vacuum chamber known as a source housing (not shown). The ion implanter system 100 may also comprise a series of beam-line components through which ions 10 pass. The series of beam-line components may include, for example, extraction electrodes 104, a 90° magnet analyzer 106, a first deceleration (D1) stage 108, a 70° magnet collimator 110, and a second deceleration (D2) stage 112. Much like a series of optical lenses that manipulate a light beam, the beam-line components can manipulate and focus the ion beam 10 before steering it towards a workpiece or wafer 114, which is disposed on a workpiece support 116.
In operation, a workpiece handling robot (not shown) disposes the workpiece 114 on the workpiece support 116 that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source 102 and extracted by the extraction electrodes 104. The extracted ions 10 travel in a beam-like state along the beam-line components and implanted on the workpiece 114. After implanting ions is completed, the workpiece handling robot may remove the workpiece 114 from the workpiece support 116 and from the ion implanter 100.
In some embodiments, it may be desirable to introduce electrons in the ion beam path, to reduce beam blowup and to reduce charge from the surface of the substrate. In some embodiments, a plasma flood gun (PFG) 117 is introduced near the workpiece 114. This plasma flood gun emits electrons into the ion beam in the direction of the workpiece 114.
In some embodiments, the electrons are produced in the plasma flood gun 117 through the use of a tungsten filament through which a current is passed. This current causes the filament to emit electrons. These electrons are then directed, such as by magnets or electrodes, to an aperture. After passing through the aperture, the electrons migrate toward the workpiece 114. The voltages needed by the plasma flood gun 117 are generated and supplied by a power supply 118. This power supply 118 may be in communication with a controller (not shown) which determined the timing and magnitude of each voltage. In some embodiments, voltages are generated for the filament, the arc and the bias within the plasma flood gun 117.
Referring to FIGS. 2A-B, there is shown one embodiment of a filament used to produce electrons. In FIG. 2A, a top view is shown, while FIG. 2B shows a side view. In this embodiment, the plasma flood gun 117 has two connection points 151, 152. A filament 153, having two contacts 154, 155 is plugged into the respective connection points 151, 152. These connection points 154, 155 are tied to different electrical potentials, thereby allowing current to flow through the filament 153. On the sides of the filament 153 are one or more magnets 156, that cause the electrons to spiral towards the walls. This spiral increases the path length of the electrons. Although not shown, electrode 157 has an aperture through which the electrons can exit. Dotted line 158 represents the emission plane in the device. The reference emission plane is related to the charging and the metals performance of the plasma flood gun 117 because the magnetic field generates specific trajectories and controls the emission points.
The lifetime of the plasma flood gun 117 is usually limited by failures of the filaments 153, which are exposed to the plasma within the plasma flood gun 117. Replacement of the filament 153 is a time consuming operation. In addition, tungsten, the preferred material for the filament 153, may contaminate the workpiece 114.
It would be advantageous if there were an apparatus and method for producing electrons in a plasma food gun, which has increases reliability, is easier to replace, and does not contaminate the workpiece or wafer.